Dental implants are becoming an increasingly popular means for restoring lost teeth in wholly or partially edentulous patients. A dental implant typically comprises a threaded titanium cylinder having a length ranging between about 5 mm and 18 mm and a diameter ranging between about 3 mm and 6 mm. Dental implants normally include an interlocking member at their gingival end for anti-rotationally connecting with a cooperating surface of a prosthodontic restoration (i.e. artificial tooth) or restoration component. These interlocking members usually take a hexagonal form, although octagonal forms are also in use. The most common type of dental implant now in use has a hexagonal post or boss (commonly called a "hex") on its gingival end which is adapted to mate with a cooperating six-sided or twelve-sided socket on a restoration component.
Dental implants are available in a variety of styles. One style is designed to install the implant substantially entirely within the patient's jawbone with its hex accessible subgingivally at the crest of the jawbone. Another style of implant incorporates a transgingival section and is installed with that section extending through the gingiva overlying the site of the implant installation. This is often referred to as a "single-stage" implant. Thus, its interlocking member is generally within or above the gingiva.
After installation, the implant is left in position for several months until it becomes integrated within the patient's jawbone (i.e. osseointegration). With the subgingival style of implant, the implant is covered by the patient's fleshy gum tissue during the osseointegration period. Thereafter, in a second stage surgery, the gum tissue is typically opened to expose an end of the implant, and a component having a transgingival section (typically called a healing abutment) is attached to the implant until the surrounding gum tissue heals around the component. After the gum tissue has healed, the transgingival component is removed to expose the interlocking member on the end of the implant, which is thereafter available to connect with a cooperating member of a dental restoration or restoration component. With the single-stage implant, a healing abutment is generally not used because the patient's gum tissue heals around the transgingival section of the implant during osseointegration. Hence, osseointegration and gingival healing in a single-stage implant occur in one, or a "single stage."
It is sometimes desirable to convert one style of implant to another style. For example, if one style is best suited for installation in a first site in a patient's jawbone, but another style is best suited for installation in another site, the restoring dentist seeking to fashion a bridge supported on implants installed in both sites might prefer to convert one style to the other in order to make a bridge using common components. Similarly, if a restoring dentist has on hand implants of one style and components for a new improved style become available, for reasons of economy it might be desirable to convert the available implants to the new styles so they can be used with the new components. Such conversion may be achieved by fitting selected transition components over the interlocking members of the respective implants, thereby forming a "converted" implant. An exemplary set of transition components is described in PCT Publication No. WO 99/17676, assigned to the assignee of the present invention and incorporated herein by reference. "Converted" implants, like "regular" implants, generally include an interlocking member at their occlusal end for mating with a cooperating surface of a prosthodontic restoration (i.e. artificial tooth) or restoration component. These interlocking members may take any form provided in a dental implant, including, for example, hexagonal or octagonal posts or sockets.
With either style of implant, or with "converted" implants, the process of fashioning the restoration usually begins with the step of attaching an impression coping to the implant and making a dental impression of the implant's site where the impression coping is affixed and of the adjacent teeth. The coping normally includes an interlocking member which will anti-rotationally connect with the interlocking member of the implant (or "converted" implant). Thus, for example, where the implant (or "converted" implant) has a six-sided "hex" post, a coping having a hexagonal or 12-point socket may be positioned on the post. A coping with a hex socket may be positioned on a hex post in only one of six possible orientations, sixty degrees apart. A finer adjustment may be achieved by using a coping fitted with 12-point sockets, which can be installed on a hex post in any one of twelve orientation positions that are thirty degrees apart.
After the coping is attached to the implant and the impression taken, the impression is removed from the patient's mouth so that it may be used to make a stone model of the patient's case. In one technique using a "pick-up" type impression coping, the coping is automatically "picked up" (i.e. removed from the implant) during removal of the impression material. In another technique using a "transfer" type impression coping, the coping remains attached to the implant during removal of the impression material, but is then removed from the implant by the clinician and "transferred" back into the impression material. Thereafter, an implant analog is attached to the coping, preferably in the exact orientation as the implant (or "converted" implant), and the stone model is made. The implant analog normally includes the same type of interlocking member as the implant itself. Thus, for example, where the implant has a six-sided "hex" post, the implant analog will normally also have a hex post. In such case, where a coping having a 12-point socket is used in the impression stage, the implant analog may be installed in the coping in any one of twelve orientation positions that are only thirty degrees apart.
One of the most important aspects of a successful restoration is that the restored tooth must be pleasing in appearance when positioned within the patient's mouth. The aesthetic aspect of the dental restoration is particularly important when a single anterior (i.e. front) tooth is being restored. Not only must a front tooth look natural at the gum line, but it must align naturally with the two adjacent teeth. A single restored tooth must neither project forward, recede rearward nor be "twisted" around the axis of the underlying implant in relation to the adjacent teeth. To that end, it is important that the orientation of the implant analog in the stone model is exactly the same as the orientation of the actual implant (or "converted" implant) in the patient's mouth. This normally requires that, in the impression stage, the connecting means on the implant analog is perfectly aligned with the connecting means on the implant (or "converted" implant) itself. If, for example, the hex of an implant analog is not perfectly aligned relative to the hex of an implant in the impression stage, a restored tooth fashioned on the implant analog will be misaligned relative to the patient's teeth, when attached to the implant in the patient's mouth.
Perfect alignment of the implant and implant analog is difficult to achieve, however, especially when impression copings having 12-point sockets are used. This is because the dentist is not able to see clearly the actual orientation of the hex of the implant analog within the 12-point socket of the impression coping. Moreover, the dentist can not reliably note the position of implant hex itself because the end hex of the implant (or "converted" implant) is quite small (about 2-3 mm between parallel flat surfaces) and can be buried relatively deeply below the gingival tissue. One of the aspects of the present invention is directed to solving or at least reducing the effects of this problem by providing a method and device for more easily orienting the implant analog with the dental implant (or "converted" dental implant) at the impression stage.